1. Field of the invention
This invention relates to transparent electrically conductive material systems.
2. Description of the Prior Art
Layers, coatings, and thin films of metal oxides which are electrically conductive are well known. These have been used extensively in the fabrication of, for example, display devices such as liquid-crystal displays wherein some of the electrodes are required to be transparent so as not to impair the viewability by an observer of the displayed information. For an example of this application, see Schindler, U.S. Pat. No. 3,814,501. The most frequently encountered metal oxides used for this purpose are oxides of indium, tin, and of indium and tin together (indium-tin-oxide or ITO). Schindler discloses patterns of transparent, electrically conductive material in a liquid-crystal display where the conductive material is indium oxide or tin oxide or a combination of these materials.
Another application for transparent electrical conductors is as electrodes for gate structures which are fabricated on such semiconductor devices as charge-coupled imagers.
In both the imager device and the display device applications, the practice has been to form the conductor pattern as a separate, discontinuous entity. Typically, the pattern has been formed by depositing metallic oxide material and then using photolithographic techniques to conform the metallic oxides to a desired conductor pattern although various other approaches such as, for example, printing have also been used. For an example of the latter, see Laurie, (West German) Offenlegungsschrift No. 2,411,872.
Where a conductor pattern of, for example, ITO is formed as a separate entity on an imager or display device, at least two distinct types of paths are created for light which is incident on the device. In one type of path, a light beam passes through the thickness of the ITO once or twice depending on whether or not it is reflected. In the other type of path, which does not pass through an ITO layer, the light typically travels a longer distance through air-filled space. The difference between the indexes of refraction of the air and ITO and the difference in the number of interfaces traversed by a light beam depending on the path traveled produces distortion in the image sensed or reflected. The subject invention greatly reduces these differences thereby reducing the resultant distortion.
Barrett et al, U.S. Pat. No. 2,932,590, discloses the controlled deposition of metallic indium and tin and the subsequent thermal oxidation thereof to produce thin, transparent, electrically conductive coatings. However, Barrett et al does not disclose the formation of a pattern of electrical conductors included in an insulative film as disclosed herein.